Frictionless hip joint

ABSTRACT

An orthopedic prosthesis includes a head which internally accommodates the major motion of a patient, e.g., during walking, thereby reducing wear against a cup or liner. A neck may be utilized which rotates within the distal member about an axis aligned with the major motion of the patient. The orthopedic prosthesis may also include a sacrificial anode, a seal made of natural fibers, and utilize lubricant made of honey.

CLAIM OF PRIORITY

The present non-provisional patent application is a continuation-in-partapplication of a currently pending and prior filed non-provisionalpatent application having Ser. No. 15/829,267 filed on Dec. 1, 2017, andwhich claims priority pursuant to 35 U.S.C. Section 119(e) to aprovisional patent application having Ser. No. 62/491,829 filed on Apr.28, 2017, the contents of which are incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention is directed to an improved orthopedic hipprosthesis as well as several advancements in the art including the useof naturally occurring, bio-compatible lubricants, seals made of naturalfibers, and the use of a sacrificial anode.

Preliminary Statement of the Invention

This device was designed to, among other things, simultaneously:

-   -   1) Significantly reduce the current incidents of hip        dislocations and the medical care that follows;    -   2) Eliminate the need for hip revision surgery;    -   3) Confine metallic wear particles away from body tissue        reducing the potential for metal poisoning to an insignificant        threat;    -   4) Increase the ability to support substantially greater weights        without component damage from friction;    -   5) Have constant and proper lubrication; and    -   6) Increase or maintain a large range of motion.

A brief statement of how the foregoing is accomplished, without limitingthe scope of the invention, follows:

Hip dislocations following hip replacement surgery have a directrelationship to the size of the femur ball head used. It was believedthat smaller ball heads produce less friction within the liner, butunfortunately a small size ball head tends to dislocate somewhat easily.It was later discovered that larger ball heads dislocated less often butincreased the surface finish damage from friction, and therefore adirect relationship to size has been established. That is, a larger theball head develops more wear on the liner because of the greatercircumference and speed of the ball head moving against the liner.Current ball head sizes are a compromise between friction damage, thepatient's anatomy, and desired range of motion.

In revision surgery, the ceramic liner that is mounted within the pelvisand receives the ball head is worn out from, among other causes, “edgeloading”. Both liner and ball head are replaced and the mating partshave a useful life of 10-20 years depending on activity. However, linerseventually break down as they rely only on the body's fluids which arean insufficient lubricant to protect against that type of edge load andwear.

Removing this ceramic liner altogether can not only eliminate revisionsurgery regarding liner replacement but allow a larger ball head (up to2.125″) to occupy that now vacated space leading to significantlyreduced hip dislocations while maintaining a large range of motion.

By moving the friction interaction that occurs between the ball head andceramic liner so as to now happen within the mechanism of the ball headitself, the invention compartmentalizes any metallic wear particles sothat they are contained safely and will avoid contaminating the body. Aproperly and/or continuously lubricated, precision bearing can withstandgreater loads before breaking down as opposed to the relatively drymetal or ceramic ball riding in a metal or ceramic socket. The presentinvention contemplates containing a built-in lubrication reservoir that,once filled, should outlive the patient. In one embodiment, the desiredlubricant may comprise tallow, a processed animal or human fat thatmelts from solid to viscous between 85° f and 104° f, which isconveniently the temperature range of humans as well. However, otherlubricants may still be used.

Description of the Related Art

The modern hip implant, while a significant technological advancement,still suffers from several deficiencies that cause complications in itsuse, lead to revision surgery, or make it vulnerable to post-operativedislocation, among other issues. The present invention addresses severaldeficiencies, while improving the life span of a hip implant, all whileproviding a familiar silhouette, such that surgical techniques need notbe modified much, if at all.

A typical hip implant procedure requires removal of a substantialportion of the femur bone, as well as preparation of the acetabulum witha “shell” or “cup” to receive the new prosthetic. The term “cup” as usedherein, may comprise a multi-component assembly including at least ashell and a liner. In general, however, the head and neck of the femuris removed and a portion of the remaining femur is hollowed out. Thefemur stem of a hip prosthesis is inserted into the hollow portions ofthe femur, the hip prosthesis having a neck and head protruding from thefemur, loosely approximating the patient's anatomical femur neck andhead. The acetabulum is prepared via a reaming process to create asocket into which a shell or cup is inserted. The cup may consist of twopieces, a shell and a liner. The shell is generally made from metal andis seated into the reamed acetabulum. The liner, which may be made ofceramic or a desired polymer, is seated into the shell and the head ofthe prosthesis is seated into the liner. The shell, as well as the stem,are rigidly secured to the patient's existing bone structure. They maybe cemented into place or be seated with an interference fit, e.g., byhammering into place. They may also include a particular surfacetreatment, such as to increase porosity, such that over time, thepatient's bone and/or tissue will naturally fuse with the shell andstem.

As may be expected, wear is of particular concern. Over the lifetime ofa patient, the head may be expected to undergo innumerable rotations andgyrations within the liner, and a substantial portion of those may beexpected to occur under loading, such as when the patient is standing,walking, running, jumping, carrying an object, etc. The weight of anobese patient can significantly accelerate wear due to increasedfriction. Thus, reduction of friction between the wear surfaces has beena significant focus within a primary field of tribology and the study ofmaterial selection for friction, lubrication, and wear characteristics.Liners are generally selected of suitable metal or polymers, such ashigh-density polyethylene (“HDPE”) or ultra-high-molecular-weightpolyethylene (“UHMWPE”). The femoral head is generally selected of ahard, brittle material, such as cobalt chromium or ceramic, which isthen polished, to further reduce wear of the liner. Suitablecombinations of materials between the liner and the head, such asmetal-on-polymer, ceramic-on-ceramic, or metal-on-metal, may havedifferent advantages or disadvantages, to be considered by medicalprofessionals.

In this context, certain disadvantages become apparent. Initially, giventhe space constraints within the acetabular region of a patient, thesize and/or thickness of the shell and liner serves to limit the overallsize of the implant. Therefore, inclusion of a liner serves to reducethe size of the femoral head that may be used and, if sufficient forceis applied, the femoral head can be leveraged out of the cup/liner.Though a larger femoral head may decrease the risk of dislocation,because the femoral head may rotate further within the socket beforeimpingement of the neck occurs on the liner, as compared to a femoralhead of smaller diameter, a larger femoral head will also lead toincreased volumetric wear from increased inertial forces. However, thelimiting factor in determining the size of the femoral head is thethickness of the liner. Accordingly, there is a need in the art for animproved prosthesis which allows a larger femoral head to be utilized.

Yet another disadvantage present in current hip implants stems from theuse of increasingly hard and highly brittle materials, a trait thoughtto be desirable as harder materials can be polished to provide lowerfriction. However, a common failure mode in hip implants is a fractureleading to catastrophic structural failures in the implant, especiallyaround the neck and femur shank. In considering that the femoral head isoffset by the neck from the femur shank, it is apparent that stressestransferred through the femur shank into the hip will cause a moment, ora torque, about the neck and/or femur shank. The repeated stressestransferred through the shank over the lifetime of the patient, coupledwith the neck-stem leverage or bending moment, may result inmicro-motion and, due to the brittleness of the materials, fatigue willlead to crack propagation and eventually failure of the prosthesis. Suchmicro-motions are a more significant problem for modular implants, wherethe head is formed of a separate component from the neck and ispress-fit onto the neck via a taper, which can be worked loose.

Yet another deficiency apparent in the modern hip implant is corrosion.In one respect, modular hip implants, such as those with separate headand neck portions, were introduced to simplify revision surgery, byoffering the ability to simply replace the head, and also allows the useof different materials where desired, such as a ceramic head, whichcannot be integrally formed with a metal neck. Alternatively,cobalt-chrome heads are selected for the material's hardness, which isideal for use as a bearing surface, especially when polished. However,the rigidity, or modulus of elasticity, of cobalt-chrome issignificantly higher than that of bone, which makes it unsuitable foruse as a femoral stem, as it would transfer significant stresses intothe bone. Hence, titanium alloys are generally selected as femoral stemcomponents. The use of multiple metals for their desirable materialtraits, however, leads to corrosion, especially at the interface of boththe head-to-neck taper, and the neck-to-stem taper where the modularunit is mounted to a femoral stem.

Mechanical corrosion, such as crevice corrosion or fretting is a commonmode. Crevice corrosion may occur at the interface of two materials and,in the context of orthopedic implants, can be caused by the breakdown ofsurface oxide layers on the prosthesis, which otherwise serve to protectthe materials from the electrochemical and saline environment of apatient's body. Fretting is the mechanical assistance of crevicecorrosion, due to a number of factors, including the repeated stressesapplied at the neck due to the leveraging of the patient's weightthrough the offset stem. As can be appreciated, the more modularity inan implant, such as those with both modular heads and necks, the morechance for debris to form due to corrosion at the modular interfaces.

The inventor herein considers that another mode of this corrosion isgalvanic corrosion. Specifically, when dissimilar metals are disposed inan electrolyte solution, such as when a cobalt chromium head is pressfit onto a titanium femur shank and disposed within the corrosive salineenvironment of a patient's body, an electrochemical cell is created. Onemetal serves as an anode, while the other metal serves as a cathode, andcorrosion at the anode is accelerated due to the difference inelectrical potential.

This effect may be amplified by the piezoelectric properties of bone,and the cyclical pressures created at the tapers, generating furthervoltage when stressed. In particular, when a patient loads the femur,such as when walking, an electromotive force is generated within thefemur, thereby causing voltage to flow. This voltage may follow a paththrough the implant and into the shell and pelvis. When combined with adissimilar metal implant acting as a cathode/anode, galvanic corrosioncan be accelerated. Moreover, or alternatively, the triboelectric effectmay cause a buildup of charged particles due to the constant rubbing ofthe ball against a dissimilar liner, further contributing to anelectrical potential generated across the implant.

This galvanic corrosion, acting in concert with mechanical corrosion, aswell as the cyclical loading causing fatigue within the implant, leadsto significant failure rates and additional complications.

With the foregoing in mind, there is a need in the field of art relatingto hip replacements for an improved device which provides for the use ofa larger femoral head, thereby reducing the occurrence of dislocation.Such a device also reduces the wear on the femoral head by transferringthe majority of motion of the prosthesis away from the acetabularinterface and thereby allows for selection of materials which are moredurable, and do not cause corrosion from dissimilar metals.Additionally, the present invention provides for greater range ofmotion, eliminates unwanted noises caused by wear, is capable ofcarrying tremendous loads without wear, and is self-lubricating.

Further advancements in the art, which are disclosed herein, include theuse of a sacrificial anode to assist in corrosion resistance of criticalcomponents, the use of naturally occurring, bio-compatible lubricants,and seals made of natural fibers. As is presently understood, galvaniccorrosion is one of the mechanisms which virtually any metallic implantmust undergo. While, the use of a sacrificial anode can preserve thecritical components of an implant, the selection and placement of such asacrificial anode must be carefully attended, otherwise the sacrificialanode will release metallic ions and other debris into the body. Thepresent invention discloses at least one arrangement for the deploymentof a sacrificial anode within an implant such that all metallic ions andparticles are trapped within the implant itself, and not released intothe body.

These and other problems present in the art are addressed in thefollowing embodiments of the present invention.

SUMMARY OF THE INVENTION

The present invention is directed to an orthopedic hip prosthesis (“hipimplant”) to be implanted within a patient that addresses several needsin the field of art relating to hip replacement. One advantage of thepresent invention is the elimination of the traditional liner, which isgenerally quite thick. Removing the liner (or in certain embodiments,significantly reducing the liner's thickness) allows for the use of alarger diameter head than would otherwise be suitable, given the spaceconstraints in the acetabular region. As is known, a larger head leadsto larger volumetric wear, especially considering that in the absence ofa liner, the head will rotate against the shell. In order to address theincreased volumetric wear, one embodiment of the present inventionproposes to internalize much of the repetitive, cyclical, rotation ofthe implant within the head. Alternatively, a substantially thinnerliner than heretofore considered suitable may be utilized in conjunctionwith the present invention.

In general principle, the present invention recognizes that the majoraxis of motion in a hip joint is that which provides rotation duringwalking and running movements. While a hip joint provides for othermotion, e.g., laterally, these motions are minor in comparison.Accordingly, one aspect of the present invention internalizes at leastthe major motion interiorly of the orthopedic prosthesis, therebysignificantly reducing the wear that otherwise occurs between the headand liner of an ordinary implant, eventually causing such complicationsas tissue necrosis or pseudo-tumors.

In at least one embodiment, the present invention is directed to acoaxial, fully articulating joint, which is particularly suitable as anorthopedic hip prosthesis, in which the head includes at least twoportions, a proximal member and a distal member. The proximal member isdimensioned and configured to be received directly by the acetabulum, orif not directly, then preferably at least by a thin shell installedwithin the acetabulum. Such a “thin shell” as may be utilized by certainembodiments of the present invention functionally replaces both theshell and liner of the prior art. The proximal member is disposed insubstantially unrestricted relation within the acetabulum in that it isfree to rotate within the acetabulum or liner, such that minor motionsof the patient's leg, e.g., lateral motions, can be accommodated whendesired.

The distal member is dimensioned and configured to be fixedly connectedto a femur of the patient. The distal member may include a shank that iseither directly installed within a femur of the patient or may becoupled to a more traditional femur stem, which is in turn installedwithin the patient's femur. The proximal member and distal member arecorrespondingly dimensioned and configured to be adjoined at a matinginterface, which may be internally of the proximal member, but whichconstrains movement of the distal member within the proximal member torotation about a single axis, i.e. a single degree of freedom ofmovement relative to the proximal member. Preferably, this single degreeof freedom of movement is coaxial, when properly implanted within apatient (or installed in a walking mechanism of, e.g., a robot), withthe patient's natural axis of rotation of the legs during walking andrunning motions. Stated otherwise, the distal member may rotate withinthe proximal member about an axis that can be aligned with the patient'snatural axis of rotation of the legs. Accordingly, the major motion ofthe patient is accommodated interiorly of the orthopedic prosthesis, anddoes not require any movement of the head within the acetabulum duringsuch major motions.

In yet another embodiment, the proximal member comprises a head thatincludes a recess, while one embodiment of the distal member comprises aneck that includes an axle. The axle may be rotationally disposed withinthe recess of the head. The axle and the head are correspondinglydimensioned and configured such that the invention may be implanted withat least the majority of the rotational axis of the axle aligned withthe natural walking axis of the patient. Accordingly, movement of theimplant due to, e.g., walking or running, causes a rotation of the axlewithin the head, while movement of the head relative to the shell isminimized, if not entirely eliminated. Movement of the head relative tothe shell is therefore only required during off-axis and/or low-loadingmovements, such as lateral motions of the patient's leg, e.g., whenputting on footwear.

Given that the majority of rotational movement is internalized withinthe head, the mating surfaces between the axle and recess may belubricated and such lubrication will be maintained within the head,rather than spreading to other parts of the patient's body. Accordingly,wear is significantly reduced, perhaps extending the life of the implantof the present invention to even longer than that of a patient. Anadditional advantage is that if debris is generated, it will be retainedinside the head, and thereby avoid complications for patients where,e.g., metal, ceramic, or polyethylene chips or filings are released intothe patient's surrounding tissue.

Furthermore, because wear is significantly reduced, and because movementof the head relative to the shell is significantly reduced, materialsmay be selected without undue concern for their wear characteristics,such as the hard, brittle cobalt chromium and ceramic utilized in modernimplants. Instead, far more durable materials, such as spring steel, maybe selected to improve the fatigue life of the implant, and avoidfractures and failures that occur when brittle materials are used.Additionally, dissimilar metals need not be utilized, as in the cobaltchromium head and titanium neck that is popular in modern implants.Accordingly, galvanic corrosion is eliminated. In yet additionalembodiments, composite materials, such as carbon fiber reinforcedpolymers may be suitable for use with the present invention as, due tothe reduction in wear, materials need not be selected for their wearproperties, be may instead be selected for strength, flexibility, ordurability.

In at least one embodiment, the axle contains a lubricant reservoir, forretaining a predetermined amount of lubricant which may be selected tolast for the life of the implant. In such an embodiment, the recess inthe head and the axle are correspondingly dimensioned and configuredsuch that lubricant may flow between the mating surfaces where therecess and axle rotate against one another. As such, the bearing createdby the axle and the recess maintains constant lubrication. Additionally,debris may be carried back to the reservoir and maintained therein. Inyet further embodiments, balls or rollers may be disposed between theaxle and recess in order to further reduce friction and support radialloading. It will be appreciated that the term “axle” as used herein,refers to the structure which may be disposed interiorly of the head,and is not meant to connote any particular geometric limitation.

In yet another embodiment, the present invention reduces micro-motionand fatigue due to repeated stresses transferred through the implantfrom, e.g., walking, running, jumping, etc. In such an embodiment a cageis provided, which is to be fixed to the distal end of the neck of thepresent invention via a bushing. In a preferred embodiment, a suitablepolymer with a damping quality is injection molded between the cage andthe distal end of the neck, thereby securing the cage to the neck andforming the bushing. The cage may then be pressed or cemented inside themodular taper of the femur stem (which is inserted into a patient'sfemur) or the neck and cage may be implanted directly into the patient,as the case may be. In either embodiment, it will be appreciated thatthe cage will provide a rigid attachment point, while the bushing servesto at least partially isolate micro-motion, and other fatigue inducingstress, from the neck, thereby reducing fractures, corrosion, andeventual failure. Cementing the cage into the femur stem seals themajority of the bushing from the patient's tissue.

In at least one embodiment, the distal and proximal members are retainedtogether via a shear interference fit of a retention member. Such aretention member should allow rotation of the distal member relative tothe proximal member, but interfere with translational movement of thedistal member relative to the proximal member. By way of non-limitingexample a circular spring retention clip may be disposed about the axleand further in at least partially interfering relation with both theinner surface of the head and the outer surface of the axle. As such,rotation of the axle within the head is provided for, yet translation ofthe axle out of the head is prevented. By way of further example, aplurality of ball bearings may be utilized instead of a spring retentionclip, which has the added benefit of reducing wear of the matingsurfaces of the head and neck. In yet further examples, one or moredowel pins or set screws may be disposed through the head and into shearinterfering relation with a channel disposed about the axle.

While the present invention has been described in the context of anorthopedic implant, and particularly intended for use as a human hip,the structure of the present invention is suitable for a variety ofother uses, such as other human or animal joints, more specificallyequestrian joints where excess weight is of concern, as well as roboticuse, and commercial and industrial use, particularly in machinery thatutilize joints with a primary direction of motion, but also requireadditional degrees of freedom.

Yet another embodiment of the invention provides a “sacrificial” or“galvanic” anode to shield critical components of the invention fromcorrosion. As described above, in the case of hip implants, the bendingof the femur under load causes a voltage flow from a piezoelectriceffect, which contributes to an electrical potential generated acrossvarious components of the implant. The triboelectric effect may alsocause a buildup of charged particles due to the constant rubbing of theball against a dissimilar liner.

Accordingly, such a sacrificial or galvanic anode may be selected from amaterial which is more anodic (i.e., having a greater electrochemicalcorrosion potential) than the materials selected for the remainingcomponents of the hip implant itself. By way of non-limiting example, ifan implant is made from steel or titanium, then a suitable anode may becomprised of zinc, aluminum, or magnesium. The anode is then placed inelectrical communication with the implant itself, such that the implantdoes not corrode prior to the anode. However, releasing metallic ionsand corrosion-related particles into the body is undesirable. In apreferred embodiment, the anode is sealed within an interior portion ofthe hip implant, such that corrosion-related particles do not escape thehip implant and are not released into the body. One such configurationis placing the anode within the aforementioned lubricant reservoir. Yetanother embodiment may comprise fastening the anode to a distal end ofthe neck and/or axle of the present invention. When referring to neck ofthe present invention, distal refers to the end of the neck that istowards the head, while proximal refers to the end of the next that istowards the shank.

In yet another embodiment, honey, and most preferably bee honey, may beselected as a desirable lubricant for the inventive hip implant. Honeyis a known preservative and this property is thought to be due to thepresence of gluconic acid and hydrogen peroxide, both of which naturallyoccur in honey, and are responsible for the higher acid content andsuppression of bacterial growth in honey. Another naturally occurringcompound in honey, Methylglyoxal or “MGO” is thought to be the primaryelement contributing to the antibacterial properties of honey. Mosttypes of honey include between 0-20 mg of MGO per kilogram of honey.Manuka honey, however, generally has at least 20 mg of MGO per kilogramof honey, but can include up to, and beyond, 800 mg of MG per kilogramof honey. Accordingly, Manuka honey is thought to be highly resistant tobacterial growth, has been shown to be effective at fighting infectionwithin the body, and would be desirable in a most preferred embodimentof the present invention.

However, honey is also susceptible to crystallization and the likelihoodof crystallization in honey is affected by the fructose to glucose ratioor “F/G ratio.” Some research suggests that honey having an F/G ratio ofless than 1.3 is likely to crystallize during long periods of storage,while ratios above are less likely to crystalize, and slower tocrystalize if it does occur. It has also been found that Manuka honeymade from Australian stingless bees generally has an F/G ratio of 1.4.Moreover, the melting point of crystallized honey tends to be between104 and 122 degrees Farenheit. When honey is utilized as a lubricant inthe present invention, it will circulate between the various movingparts of the invention (such as the axle, bearings, roller bearings, andinner surface of the head). Accordingly, any such crystallization wouldbe worked and heated by the kneading and milling action between thevarious moving parts and will be amalgamated back into its liquid form.

Additionally, honey is an electrical conductor due to its electrolytecontent in the form of various minerals and acids. Because of thisconductivity, honey may act as an electrical conductor of thepiezoelectric and triboelectric voltage generated outside the implant toa sacrificial anode installed inside of the device, thereby facilitatingthe corrosion resistance of such an embodiment. It is due to thesequalities of honey, and others, that it is desirable as a life-longlubricant for the present invention. In a preferred embodiment, honey isinjected in an amount and with pressure sufficient to fill the recess inthe head to capacity, displacing all air from within the working bearingchamber.

Finally, the viscosity of honey does not preclude its use as alubricant, as normal use of the prosthetic does not require large speeddifferentials between the various moving components of the hip implant.As such, significant shear forces within the honey, and thereforefrictional losses due to “drag,” are not anticipated.

Moreover, selection of a lubricant with a relatively high viscosity mayprovide an additional benefit. If a very low viscosity lubricant wereutilized, frictional forces between the head and the axle may never besignificant enough to cause the head to rotate within the acetabularregion under no load. As such, the head would essentially be heldcaptive by the relatively larger frictional forces between the head andthe acetabular region, while the internal moving parts of the implant(such as the roller bearings and ball bearings) would constantly rockback and forth on essentially the same spot within the head, leading toaccelerated wear within the head, including any bearings therein.

On the other hand, the viscosity of the lubricant may be selected suchthat the forces required to rotate the axle within the head are higherthan the forces required to rotate the head within the acetabular regionwhen the implant is not bearing the patient's weight. Accordingly, asthe patient moves a leg forward (not under load) while walking orrunning, the head will tend to rotate within the acetabular region,while the axle will tend to be held captive within the head. At the sametime, when the implant is bearing the patient's weight, frictionalforces between the acetabular region and the head of the implant areincreased, and careful selection of the lubricant's viscosity can resultin an arrangement whereby the head is then held stationary within theacetabular region by the increased forces, while the axle rotates withinthe head to accommodate the patient's stride. Such an arrangement willresult in a rotational migration of the head within the acetabularregion akin to a ratcheting mechanism. As the patient strides forwardwith the implant unloaded, the head will rotate within the acetabularregion. When weight is applied to the implant, frictional forces betweenthe head and the acetabular region are increased, which tend to hold thehead captive, while the axle is free to rotate within the head. In suchan embodiment, a “new” or different portion of the head is presentedwithin the acetabular region on each stride. As such, the internalmoving parts of the implant (such as the roller bearings and ballbearings) are constantly introduced to a “new” or different portion ofthe inner surface of the head as well, which spreads mechanical wear outover the entire surface of the implant.

In a typical prior art hip implant, the head of a hip implant does notrotate independently of the neck portion and spans approximately 58degrees of contact within an acetabular region or cup. As such, onlyabout one sixth of the surface area of the head is utilized as a “wearsurface.” The present invention permits the entire 360-degree span ofthe head to be utilized as a wear surface due to the independentrotation of the head and neck. Accordingly, mechanical wear of thepresent invention can be reduced by at least a factor of six relative toprior art hip implants due to selection of a lubricant having sufficientviscosity. Other features of the present invention further reduce wearand enhance the service life of the inventive hip implant.

In additional embodiments, the viscosity of the lubricant may beselected to achieve different rotational characteristics. Whilerelatively high viscosities will produce substantially unidirectionalmovement of the head within the acetabular region, lower viscosities mayproduce bidirectional movement of the head within the acetabular region,as may be desired.

In yet another embodiment of the present invention, it may be desirableto provide a seal made from natural fibers and/or animal hide, such asleather, in place of a synthetic seal. Synthetic seals, such as thosemade from butyl and silicone, tend to form a smooth, glossy skin on theouter surface of the seal. Seals which are to be used in relatively highpressure applications require a harder material and high machinetolerance, while softer seals are more compliant to varying dimensionalchanges. Over time, synthetic seals, especially those made frominjection molding processes, will wear at the point(s) of contact,eventually breaking the skin and disintegrating over time. The polymersthat make up synthetic materials also tend age over time and becomebrittle leading to yet another mode of failure.

On the other hand, leather is highly resistant to wear and tearing, hasa relatively low coefficient friction, and is non-abrasive. Accordingly,when disposed against moving parts, leather can be expected to maintaina long working lifespan. Additionally, leather generally contains smallsurface wells that can be impregnated with different materials, such aslubricant(s) including honey. A single leather seal can last beyond theservice life of a typical hip implant, especially if kept wet. Yetanother benefit of leather is that once wet, it tends to swell.Accordingly, if sized appropriately, an initially dry leather seal canswell to tolerance if placed in a wet environment. Furthermore, incertain embodiments of the invention, any lubricant placed in thereservoir will displace all air in the reservoir, and thus create aslight vacuum when the unit is sealed. Accordingly, such a leather sealneed only form a barrier of separation between the lubricant and thebody in which the implant is disposed. It is for these reasons that apreferred embodiment of the present invention utilizes a seal or gasketmade of leather, and not from synthetic materials.

These and other objects, features and advantages of the presentinvention will become clearer when the drawings as well as the detaileddescription are taken into consideration.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature of the present invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a perspective view of an orthopedic hip prosthesis inaccordance with one embodiment of the present invention.

FIG. 2 is an exploded perspective view of an orthopedic hip prosthesisin accordance with one embodiment of the present invention.

FIG. 3 is a perspective view of an orthopedic hip prosthesis inaccordance with one embodiment of the present invention.

FIG. 4 is a section view taken along line 4-4 of FIG. 3.

FIG. 5 is a side perspective view of an orthopedic hip prosthesis inaccordance with another embodiment of the present invention.

FIG. 6 is a rear perspective view of the orthopedic hip prosthesisdepicted in FIG. 5.

FIG. 7 is a section view taken along line 7-7 of FIG. 6.

FIG. 8 is a perspective view of a distal member according to oneembodiment of the present invention.

FIG. 9 is an exploded perspective view of an orthopedic hip prosthesisaccording to yet another embodiment of the present invention.

FIG. 10 is a front plan view of the orthopedic hip prosthesis depictedin FIG. 9

FIG. 11 is a partial section view taken along line A-A of FIG. 10.

Like reference numerals refer to like parts throughout the several viewsof the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 1-4, one embodiment of the present invention isdirected to an orthopedic hip prosthesis 10 including a proximal member11 and a distal member 12, as best shown in FIG. 2. The head 100 is asubstantially spherical member, which approximates the geometry of atraditional hip replacement prosthesis with notable exceptions. The head100 will be generally of a larger diameter than its modern equivalentsdue to the elimination of the “traditional” liner, which tends to bequite thick in dimension, and shell (or, in certain embodiments,replacement of the “traditional” liner and shell with at least a thinshell). Additionally, the head 100 includes a recess 110, such as shownin FIG. 2, with the recess 110 having an inner surface 111.

Another component of the orthopedic hip prosthesis 10 is the neck 200.The neck 200 of the depicted embodiment includes an axle 210, as shownin FIG. 2, which has an outer surface 214. As may be seen, the axle 210is correspondingly dimensioned and configured with the recess 110 to beinserted therein, with the outer surface 214 and inner surface 111defining a mating interface 2000 between the head 100 and the neck 200,as best shown in FIG. 4. The neck 200 may also include a shank 220,shown in FIG. 2, which may be either implanted directly into thepatient's femur, supplanting the need for a traditional femur stem, orcombined with a traditional femur stem, either integrally or modularly.

In certain embodiments, and with reference to FIG. 4, the neck 200 mayalso include a contour 215 (or 215′ as depicted in later Figures)disposed between the axle 210 and shank 220. The contour 215 may bedimensioned and configured to provide a substantially flush mountbetween the neck 200 and head 100. The contour 215 may also begeometrically configured to facilitate a substantially smooth transitionfrom head 100 to neck 200, e.g., in the scenario of extreme lateralmovement of the patient (such as raising one's leg sideways) where theneck 200 may otherwise impinge on the thin shell 4000 (if used) or otherstructure, such as the acetabular region of the pelvis. It will beappreciated that the thin shell 4000 depicted in the Figures ispresented for purposes of facilitating the structure and operation ofthe present invention, and that a thin shell 4000 utilized inconjunction with the present invention need not conform to theparticular structure or dimensions thereof.

Certain embodiments of the neck 200 and head 100 may also include areservoir 211, as shown in FIG. 4, which may be formed by providing oneor more recesses and/or reliefs within the head 100 and neck 200, suchthat a reservoir 211 for lubricant is created and sufficient room isprovided for the lubricant to flow to and from the mating interface2000. In one embodiment, the lubricant may be comprised of human oranimal tallow, which, depending upon its various characteristics, may besolid at room temperature, but have a melting point below or near 98degrees Fahrenheit, which in turn, makes it suitable for packing thereservoir at room temperature, yet facilitating a lubricant bath withinthe head 100 once warmed by the patient's body. Alternatively, vitaminE, hydrolyzed collagen gelatin, or a dry lubricant can be used. As maybe appreciated, the lubricant should be selected such that, if a leakoccurs, the patient's tissue will not be negatively impacted.Additionally, the reservoir, and other negative space within theprosthesis 10, should be packed until no air remains in order to furtherreduce the likelihood of leaks. In some embodiments the reservoir 211may be packed manually. Additionally, as is depicted in alternativeembodiments herein, a lubricant channel may be provided such that thereservoir may be packed from the exterior of the head 100, e.g., byusing a syringe to force lubricant into the reservoir 211 and othernegative space, thereby eliminating any air pockets. Specifically, if noair remains in the negative spaces, suction would hold the viscouslubricant within the prosthesis 10.

In yet further embodiments, the neck 200 is rotationally secured withinthe head 100 via a spring retention clip 300. In the depictedembodiment, both the head 100 and neck 200 have correspondinglydimensioned and disposed retention clip channels 213, 114 (as bestdepicted in FIG. 4). The retention clip 300 will be preselected suchthat it may be compressed about the axle 210 when the neck 200 isinstalled within the recess 110. When the retention clip 300 is movedinto alignment with the retention clip channel 114 in the head, theretention clip 300 will expand at least partially into the channel 114,thereby fixing the neck 200 within the head 100, yet allowing the neck200 to rotate about its axis of rotation 1000.

With reference now to FIGS. 5-8, a rotationally free, buttranslationally secure mounting of the neck 200′ within the head 100′ isaccomplished via a plurality of ball bearings disposed about the neck200′ in at least partially shear-interfering relation with the neck 200′and head 100′. More specifically, the head 100′ and neck 200′ are matedso as to rotate relative to one another, but are constrained fromtranslational movement. As can be seen, the plurality of ball bearingsfacilitate such rotational movement of the neck 200′ within the head100′, but substantially preclude translational movement of the neck 200′relative to the head 100′, due to the interference created by theplurality of ball bearings. With reference to FIG. 7, the retentionchannel 213′ is at least partially disposed within the head 100′ and atleast partially disposed within the neck 200′. As such, when one or moreball bearings are disposed within the retention channel 213,translational movement of the head 100′ relative to the neck 200′ isprecluded via the shear-interfering relation of the ball bearings withinthe retention channel 213.

In order to facilitate assembly of the present invention, a bearingpassage 240′ (see FIG. 7) may be provided which is in communication withboth the retention channel 213 as well as the exterior of the neck 200′.Once the neck 200′ is inserted within the head 100′, the plurality ofball bearings 600 may be inserted into the bearing passage 240 andallowed to travel into and around the retention channel 213′. Once theretention channel 213′ is packed with ball bearings 600, a plug 240and/or set screw 242 is inserted to maintain the ball bearings 600within the retention channel 213′.

As can also be seen with reference to FIG. 7, a lubricant channel 230 isprovided which facilitates communication of the reservoir 211′ with theexterior of the assembly. In such an embodiment, the lubricant may beintroduced via the channel and allowed to overflow the channel,backfilling the regions around the rollers 400 and ball bearings 600until no air is present within such regions. A gasket 213 may beprovided to prevent the lubricant from traveling any further, and theplug 240 and/or set screw 242 precludes the lubricant from travelingback out of the lubricant channel 230.

Additionally, and as best shown in FIG. 8, the distal member 12′includes a neck 200′ which provides for the use of rollers 400. Thoughonly a certain number of rollers are depicted, it will be appreciatedthat as many as desired may be utilized, the limiting factors being thediameter of the rollers and the circumference of the axle 210′. In orderto accommodate rollers 400, a relief 218 is provided within the axle210, but it will be appreciated that other configurations may provideequivalent functionality.

As can also be seen in FIGS. 7 and 8, some embodiments of the inventionmay have an additional component, namely a cage 500 is provided to bemounted to the end of a shank 220′. The cage 500 may be mounted to theshank 220′ via a suitable, non-rigid adhesive. In a preferredembodiment, the cage 500 is held in spaced relation to the shank 220′and then a non-rigid polymer, such as polyurethane, is injection moldedthrough the sprue passages 511 and allowed to flow between the neck 200′and cage 500′, and out of the apertures 510, thereby forming a bushing.In this regard, a stable but flexible connection is formed between thecage 500 and the neck 200′. As such, stresses transferred through afemur shank to the neck 200′ are absorbed by the dampening quality ofthe polymer bushing disposed between the cage 500 and neck 200′.

Turning now to FIGS. 9-11, yet another embodiment of an orthopedic hipprosthesis 10″ is disclosed. According to the disclosed embodiment, theinvention includes a proximal member 11″ including a head 100″, as wellas a distal member 12″ including a neck 200″. The plurality of the ballbearings 600″ and retention channel 213′ are disposed on a proximal endof the neck (closer to the head 100″), such that they are disposedfurther within the recess 110″ of the head 100″ relative to previouslydisclosed embodiments. Such an arrangement provides more room forrollers 400″ and/or a seal 260″.

Additionally, as can be seen in FIG. 11, the bearing passage 240″ andlubricant channel 230″ may be combined into a single structure, whichextends from a distal side of the neck 200″ (i.e., further away from thehead 100″) to the retention channel 213′ itself. Such an arrangementfacilitates assembly of the present invention. In particular, the neck200″ may be inserted into the recess 110″ of the head 100″, and then aplurality of ball bearings 600″ can be inserted into the bearing passage240″ and allowed to settle within and around the retention channel 213′.Because the retention channel 213′ includes corresponding structure onboth the neck 200″ and the inner surface 111″ of the head 100″, thebearings will then perform a “locking” function, as any attempt toremove the neck 200″ from the head 100″ after insertion of the bearings600″ will cause the bearings 600″ to interfere against the retentionchannel 213′ in what has been previously described as ashear-interfering relationship.

Once the plurality of bearings 600″ are inserted, a lubricant may beinjected via the lubricant channel 230′ with sufficient volume andpressure to cause the lubricant to fill the lubricant channel 230′, theretention channel 213′, any reservoirs within the neck 200″, the variousinterstices between bearings 600″ and rollers 400′, and force anyremaining air out past the seal 260. Once a suitable plug 241′ isinserted, the entire recess 110″ within the head 100″ is then completelyevacuated of air, and a slight vacuum is created, particularly if thehead 100″ attempts to separate from the neck 200″, which is beneficialto trapping lubricant (and any particulate matter) within the recess110″ itself. As described above, such a lubricant may comprise anaturally occurring, bio-compatible fluid such as honey, bee honey, andmost preferably, Manuka bee honey.

The present invention also makes use of a seal 260, which in a preferredembodiment may be made of a naturally occurring, suitably durable fibersuch as leather. The seal is disposed in an annular channel runningcircumferentially about the axle 210″. As disclosed above, if a liquidlubricant is utilized, the leather may absorb some of the liquid andswell to tolerance. Accordingly, when first packing the device with ballbearings 600″ and lubricant, the device may leak until the seal 260 isable to sufficiently swell and form a liquid barrier.

With specific reference to FIG. 11, an anode 270 is also fastened to adistal end of the neck 200″. In the depicted embodiment, the anode 270comprises a threaded fastener to facilitate sufficient contact with theneck 200″. In a most preferred embodiment, the anode 270 may becomprised of aluminum, magnesium, or zinc. As can be seen, fastening theanode 270 to a distal end of the neck 200″ results in disposition of theanode deep within the recess 110″ of the head 100″. As such, metallicions and other particles released from the anode 270 as it corrodessacrificially are trapped within the recess 110″. Due to the slightvacuum created when lubricant is introduced in a most preferredembodiment, any such metallic ions and other particles will tend to staywithin the recess 110″ and will not be motivated to travel outside ofthe prosthesis 10″ itself.

Since many modifications, variations and changes in detail can be madeto the described preferred embodiment of the invention, it is intendedthat all matters in the foregoing description and shown in theaccompanying drawings be interpreted as illustrative and not in alimiting sense. Thus, the scope of the invention should be determined bythe appended claims and their legal equivalents.

What is claimed is:
 1. An orthopedic hip prosthesis comprising: aprosthetic femoral neck sized and configured to be fixedly connected toa femur of a patient, the prosthetic femoral neck including acylindrical axle extending from a proximal end and a femoral shankextending from a distal end, said axle defining an outer circumferentialsurface; a prosthetic femoral head configured to be rotationallyconnected to said prosthetic femoral neck, said prosthetic femoral headcomprising a cylindrical recess defining an inner circumferentialsurface, wherein the axle of the prosthetic femoral neck is rotationallyengaged within the recess of the prosthetic femoral head; a plurality ofball bearings positioned on a proximal end of the neck between saidouter circumferential surface of said axle and said innercircumferential surface of said recess, said plurality of ball bearingsdisposed to restrict translational movement of said prosthetic femoralneck relative to said prosthetic femoral head, said plurality of ballbearings being retained inside an annular retention channel; a pluralityof roller bearings positioned between said outer circumferential surfaceof the axle and said inner circumferential surface of the recess, theplurality of roller bearings disposed to support rotational movementbetween the prosthetic femoral head and the prosthetic femoral neck; anda naturally occurring, bio-compatible lubricant disposed within saidorthopedic hip prosthesis between said cylindrical recess and saidcylindrical axle, wherein said naturally occurring, bio-compatiblelubricant comprises bee honey, wherein said annular retention channel isdisposed proximally of said plurality of roller bearings on said neck,wherein said prosthetic femoral head and said prosthetic femoral neckare configured to accommodate coaxial motion of a hip joint.
 2. Anorthopedic hip prosthesis as recited in claim 1 further comprising abearing passage, said bearing passage in communication with said annularretention channel at one end.
 3. An orthopedic hip prosthesis as recitedin claim 2 wherein the other end of said bearing passage is disposed incommunication with a distal side of said neck.
 4. An orthopedic hipprosthesis as recited in claim 1 further comprising a seal disposedcircumferentially about said neck, distally of said plurality of rollerbearings on said neck.
 5. An orthopedic hip prosthesis as recited inclaim 4 wherein said seal is comprised of naturally occurring fibers. 6.An orthopedic hip prosthesis as recited in claim 5 wherein said sealswells to tolerance when wet.
 7. An orthopedic hip prosthesis as recitedin claim 5 wherein said seal is comprised of leather.
 8. An orthopedichip prosthesis as recited in claim 1 further comprising a sacrificialanode disposed in communication with at least one of said neck and saidhead.
 9. An orthopedic hip prosthesis as recited in claim 1 furthercomprising an aluminum fastener disposed within the neck on a proximalend thereof.
 10. An orthopedic hip prosthesis as recited in claim 1wherein said honey comprises Manuka honey.
 11. An orthopedic hipprosthesis as recited in claim 1 wherein said honey contains at least 20milligrams of methylglyoxal per kilogram of said honey.